Geometric volume control corneal refractive therapy contact lens

ABSTRACT

A contact lens for treating myopia of an eye of a patient comprises an anterior surface; and a posterior surface having a semi-meridian defining: a central compression zone to contact the pretreatment cornea, a volume control zone peripheral to the central compression zone, a secondary compression zone to contact the pretreatment cornea, wherein the secondary compression zone is peripheral to the volume control zone, a peripheral relief zone peripheral to the secondary compression zone, a landing zone to contact the pretreatment cornea, wherein the landing zone is peripheral to the peripheral relief zone, and an edge terminus peripheral to the landing zone.

DESCRIPTION OF RELATED ART

The disclosed technology relates generally to contact lenses, and moreparticularly some embodiments relate to contact lenses and non-surgicalmethods for reshaping the cornea of an eye to treat visual acuitydeficiencies.

BACKGROUND

Rigid contact lenses were commercialized more than 60 years ago. Initialfitting concepts quickly evolved to bi-curve and tri-curve designs tofacilitate the required lens movement for tear exchange in lenses thatwere not gas permeable. Lens movement with the blink was imperative toallow a fresh tear layer to move from the tear meniscus at the lower lidto beneath the lens. The simple lathes used in the first two decades ofcommercialization allowed for concentric curves which were blended toavoid sharp junctions.

The central radius of the lens was selected in relationship to thecentral corneal curvature. The base curve radius could be equal to,greater than, or shorter than the central corneal curvature based on thephilosophy of the design. The radius of the first concentric zone(secondary curve) was always greater than the base curve radius and theradius of each consecutive zone peripheral to the more medial zone wasalso respectively greater than the zone just medial to it. Lenseshistorically had three or more zones. All zones outside the centraloptic zone where, as a rule, greater in radius than the underlyingcorneal radius. This was a requirement to facilitate lens movement andtear exchange.

Lenses of these designs demonstrated movement with the blink and withlateral eye movement as great as 1.0 to 1.5 mm. Adaptation was requiredto become accustomed to the movement. Edge design was also veryimportant to achieve comfort and prevent trauma to the bulbar andpalpebral conjunctiva.

The advent of gas permeable materials reduced the need for the highdegree of movement and the radial and axial edge lift that was requiredin non-gas permeable lenses. Even so, the traditional design conceptswere perpetuated and used with the new materials. Over time, the lenseswere designed to have less clearance. In the original designs it wascommon to have a secondary curve radius that was of the order of 1.4 mmgreater than the base curve radius, while in the gas permeable designsthey trended toward 0.8 mm greater than the base curve radius. The meandifference of the base curve radius from the central corneal radius alsotrended in the shorter direction.

In the last decade the mean overall diameter has also trended in thelarger direction. As a result, the modal modern gas permeable lens islarger and more closely aligned with the cornea. Early non-gas permeablelenses made of polymethylmethacrylate (PMMA) were designed to have axialedge lift approaching 100 microns while modern lenses may have as littleas 50 microns of axial edge lift. Modern gas permeable lenses alsodemonstrate movement of the order of 0.25 mm or less as compared to 1.0to 1.5 mm in early PMMA lenses.

Even so, the contemporary design concepts and teaching continue to useconcentric zone features and their respective modulation. Lenses anddesign programs refer to each zone width and local radius. Educationcurricula teach the modulation in terms of making the radii “flatter” or“steeper” and “narrower” or “wider”. Since there exists no commonlyavailable precise metrology for measuring the actual clearances oflenses and since the determination of the fit is by way of sodiumfluorescein observations, the assessment of the fit is a learned artrather than a measurement-based science.

At the same time market dynamics demand efficient time management in thefitting of contact lenses. Chair time must be reduced, and first-timesuccess rates are an important metric for productivity and optimizedchannel economics. Lens fitting concepts must be simple and must demandless training for a successful outcome.

The rigid gas permeable lens designs for overnight corneal reshapinghave progressed primarily by way of rational fitting systems where theparameters of pre-determined zones are modulated to control the apicallens radius to the apical corneal radius relationship, the midperipherallens sagittal depth and midperipheral corneal sagittal depthrelationship and the alignment of the periphery of the lens to theperipheral cornea. Those skilled in the art know that the cornea is notrotationally symmetrical and yet all commercialized lens designs arerotationally symmetrical. The result of placing a rotationallysymmetrical lens on a rotationally asymmetrical cornea is lensdecentration. Random treatment accuracy is also an undesired outcome.

Extensive and persistent efforts have been made to fit theserotationally asymmetric eyes having significant irregular elevationdifferences with lenses that are rotationally symmetrical. In somecases, toric peripheral designs or dual elevation designs are used toaccommodate orthogonal corneal elevation differences. There is a needfor non-orthogonal elevation control that is achieved by designinglenses with individual semi-meridian elevation control points. Eachsemi-meridian of the lens can be designed to have pre-determinedelevations at the respective control points defined by their distancefrom the geometric center of the lens. The elevation or sagittal depthof each point from the geometric center of the back of the lens isdetermined by the topography of the underlying respective eye at thesame location and the design philosophy algorithm describing the desiredsagittal depth relationship. These elevation differences are intended tocorrespond to the irregular elevation of the underlying cornea when thelens is applied to the eye.

Unfortunately, the standard design paradigm of using concentric curveswould result in a non-centered lens having its contact with the corneasomewhere near the corneal apex and a random volume of tear fluid underthe secondary reverse curve along with a variable contact of the lens tothe cornea in the alignment zone in the periphery of the lens. Theoutcomes with the second generation overnight corneal reshaping lensesinclude induced higher order aberrations and the inability to accuratelyand consistently create the mid peripheral power needed for consistentmyopia control. While attempts could be made to manage the cornealasymmetry with the second-generation designs, their use of co-axialconcentric radii of curvature is inherently self-limiting. The precisionand ability to experience consistency in fitting is questionable.

The same limitations are inherent in the third-generation design thatincorporates a third order polynomial in the second zone of the lens.The manufacturer of the third-generation design has not commercializedthe design in which the third order polynomial is varied bysemi-meridian to produce a rotationally asymmetric elevation and therespective regulatory approvals do not include the use of individualsemi-meridian elevation control. Furthermore, the third-generationdesign does not teach controlling the volume between the untreatedcornea and the lens in the mid-periphery of the lens, having acontrolled inward facing angle for a secondary compression zone of thelens, or having a secondary clearance zone to allow a mid-peripheralcorneal contact region to compress into the cornea.

The problem remains that the skill level of the fitter must be high andexhaustive fitting sets or lens re-orders are required to find anoptimum fit even when a third-generation lens design addresses thesemi-meridian specific sagittal depths.

SUMMARY

Embodiments of the apparatus and method may include one or more of thefollowing features. Some embodiments comprise a posterior surface of acontact lens having a shape determined to geometrically control the areain at least a single semi-meridian of the space between the surface ofthe contact lens and an underlying corneal surface defined by a firstradial location on the posterior surface and a second radial location ofthe posterior surface and the same radial locations of the cornealsurface to be treated. Some embodiments comprise a posterior surface ofa contact lens that is has a predetermined inward facing angle from apoint of contact of a mid-peripheral portion of the lens with theunderlying corneal surface to be treated that forms the peripheralaspect of the geometrically controlled area of the space between theposterior surface of the contact lens and the underlying cornealsurface.

In general, one aspect disclosed features a contact lens for reshaping apretreatment cornea of an eye of a patient, comprising: an anteriorsurface; and a posterior surface having a semi-meridian defining: acentral compression zone to contact the pretreatment cornea, a volumecontrol zone peripheral to the central compression zone, a secondarycompression zone to contact the pretreatment cornea, wherein thesecondary compression zone is peripheral to the volume control zone, aperipheral relief zone peripheral to the secondary compression zone, alanding zone to contact the pretreatment cornea, wherein the landingzone is peripheral to the peripheral relief zone, and an edge terminusperipheral to the landing zone.

Embodiments of the contact lens may include one or more of the followingfeatures. In some embodiments, a radius of the central compression zoneis spherical. In some embodiments, a radius of the central compressionzone is aspherical. In some embodiments, a diameter of the centralcompression zone is between 3.0 and 7.0 mm. In some embodiments, thevolume control zone is defined by at least four geometric control pointsconnected by one of: a spline, a polynomial, or a combination of conicsections and uncurved segments, a second geometric control point isperipheral to a first geometric control point; a third geometric controlpoint is peripheral to the second geometric control point; and a fourthgeometric control point to contact the pretreatment cornea, wherein thefourth geometric control point is peripheral to the third geometriccontrol point. In some embodiments, the first geometric control point ofthe volume control zone is positioned to have a z-axis separation fromthe pretreatment cornea in a range of 5 and 80 microns. In someembodiments, the second geometric control point of the volume controlzone is positioned to have a z-axis separation from the pretreatmentcornea that defines a predetermined area between the posterior surfaceand the pretreatment cornea in the volume control zone. In someembodiments, the third geometric control point of the volume controlzone is positioned to define a predetermined angle between (i) a lineconnecting the third and fourth control points and (ii) a horizontalline through the fourth control point. In some embodiments, a semi-chordradial distance of the fourth geometric control point is in a range of2.6 mm to 5.2 mm. In some embodiments, the secondary compression zonehas a width in a range of 0.2 mm to 0.8 mm. In some embodiments, thesecondary compression zone is defined by a shape having at least onecontrol point within the secondary compression zone, the shape definedby one of: a spline; a polynomial; or a convex conic section. In someembodiments, the peripheral relief zone is defined by at least onecontrol point positioned to have a z-axis separation from thepretreatment cornea that is at least 6 microns per diopter of attemptedreduction of central refractive error. In some embodiments, theperipheral relief zone has a width of between 0.4 mm and 1.2 mm. In someembodiments, the peripheral landing zone is defined by a shape having atleast one control point within the peripheral landing zone, the shapedefined by one of: a spline; a polynomial; a conic section; an angledcurved section; or an angled uncurved section. In some embodiments, anedge terminus of the posterior surface commences at the most radiallyperipheral aspect of the peripheral landing zone and connects to themost peripheral aspect of the anterior surface; and the edge terminus ofthe posterior surface is defined by: an ellipse, a conic section, or aspline. In some embodiments, the volume control zone and the secondarycompression zone are defined by a single spline.

In general, one aspect disclosed features a method for defining acontact lens to be manufactured for an eye of a patient, the methodcomprising: selecting, according to corneal topography of the eye of thepatient: a base curve radius of a central compression zone of thecontact lens, a peripheral semi-meridian radial distance of the centralcompression zone of the contact lens, an area of a volume control zoneadjacent to the central compression zone, and a semi-chord radialdistance of a secondary compression zone to contact a pretreatmentcornea of the eye, wherein the secondary compression zone is adjacentand peripheral to the volume control zone; determining locations of aplurality of control points to define at least the central compressionzone width, the shape of the volume control zone to produce apre-determined area between the surface of the zone and the surface ofthe cornea to be treated, the semi-meridian radial distance of thesecondary compression zone, the inward facing angle formed at the apexof the secondary compression zone; and defining a semi-meridian of aposterior surface of the contact lens according to the plurality ofcontrol points.

Embodiments of the method may include one or more of the followingfeatures. Some embodiments comprise locating a first one of the controlpoints at the geometric center of the contact lens and the correspondinggeometric center of the pretreatment cornea. Some embodiments comprisedetermining the base curve radius according to manifest refraction andkeratometry or topographic measurement of the eye; selecting asemi-chord radial distance of a second one of the control points as aperipheral terminus of the central compression zone; and setting asagittal depth of the second one of the control points at the sagittalsag of the selected base curve radius at the selected semi-chord radialdistance of the second one of the control points while the first one ofthe control points is in contact with the underlying pretreatmentcornea. Some embodiments comprise selecting a semi-chord radial distanceof a third one of the control points to separate a first region of thevolume control zone and a second region of the volume control zoneperipheral to the first region of the volume control zone; and setting asagittal depth of the third one of the control points at a distanceequal to the distance of a lens having a predetermined diopter treatmenttarget radius when placed on a mean pretreatment cornea. Someembodiments comprise selecting a semi-chord radial distance of a fourthone of the control points equal to the semi-chord radial distance of anapex of the secondary compression zone according to a desiredmid-peripheral add location. Some embodiments comprise selecting asqueeze angle of a peripheral aspect of the second region of the volumecontrol zone; and locating a fifth one of the control points to definethe squeeze angle with the fourth one of the control points. Someembodiments comprise determining a location of a sixth one of thecontrol points according to the selected area of the volume control zoneaccording to the desired mid peripheral add power. Some embodimentscomprise determining an overall diameter of the contact lens accordingto a corneal diameter of the pretreatment cornea; and determining alocation of a seventh one of the control points according to the overalldiameter of the contact lens. Some embodiments comprise determining aneighth one of the control points to define a medial aspect of a landingzone to contact the pretreatment cornea according to the cornealtopography of the eye and the desired radial distance from the seventhone of the control points according to the desired radial width of alanding zone. Some embodiments comprise selecting a diameter of a ninthone of the control points; selecting an area of a peripheral relief zonebetween the secondary compression zone and the landing zone; anddetermining a sagittal depth of the ninth one of the control pointsaccording to the selected area of the peripheral relief zone oraccording to the targeted treatment in diopters.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The figures are provided for purposes of illustration only andmerely depict typical or example embodiments.

FIG. 1 is a plan view of a posterior surface of a contact lens accordingto some embodiments of the disclosed technologies.

FIG. 2 illustrates a semi-meridian to define a posterior surface of anexample contact lens according to some embodiments of the disclosedtechnology.

FIG. 3 is a flowchart illustrating an overview process for producing acontact lens for corneal reshaping according to some embodiments of thedisclosed technologies.

FIGS. 4A and 4B are a flowchart illustrating an overview process fordefining a contact lens for corneal reshaping according to someembodiments of the disclosed technologies.

FIG. 5 depicts a block diagram of an example computer system in whichembodiments described herein may be implemented.

The figures are not exhaustive and do not limit the present disclosureto the precise form disclosed.

DETAILED DESCRIPTION

Embodiments of the disclosed technology provide corneal refractivetherapy (CRT) contact lenses for overnight corneal reshaping, andmethods for defining the CRT contact lenses using geometry volumecontrol techniques. These techniques employ spline mathematics or othergeometry to determine the surface contour of a contact lens atpredetermined control points or knots on the posterior surface of thelens defined by their specified semi-chord radial distances from thecenter of the lens to the edge of the lens and their sagittal depth froma reference plane. Some embodiments employ the corneal topography ofeach eye to apply algorithms for determining the semi-meridian sagittaldepth at each control point to allow for empirical ordering andobservational fitting of an eye for overnight corneal reshaping. Thedescribed embodiments ensure central cornea radius change to correctpre-existing myopia while producing a desired mid-peripheral add powerand mid-peripheral add location through the empirical selection of thebase curve radius of the lens while also empirically selecting thesurface elevation of the lens in each semi-meridian at multiplepre-determined control points on the surface of the lens from the centerof the lens to the edge of the lens.

FIG. 1 is a plan view of a posterior surface of a contact lens accordingto some embodiments of the disclosed technologies. Referring to FIG. 1 ,the posterior surface of the contact lens includes multiple annularzones including a central compression zone (CCZ), a first region of avolume control zone (VCZR1), a second region of the volume control zone(VCZR2), a secondary compression zone (SCZ), a peripheral relief zone(PRZ), and a landing zone (LZ). Each of these zones are described indetail below.

FIG. 2 illustrates a semi-meridian to define a posterior surface of anexample contact lens according to some embodiments of the disclosedtechnology. In FIG. 2 , the semi-meridian of the contact lens is shownas a continuous solid line having several curves and control points CP.Also shown in FIG. 2 is a pretreatment cornea, shown as a dotted line.The contact lens, and the pretreatment cornea, are plotted on a gridgraduated in millimeters. However, FIG. 2 is not drawn to scale. Itshould be understood that the particular values for the control pointsCP shown are presented by way of example only, and that othersemi-meridians of the contact lens, and semi-meridians of other contactlenses, may have different values for the control points CP. Were theeye rotationally symmetric, the contact lens could be fabricated usingonly the control points of a single semi-meridian. But as eyes are notrotationally symmetric, the control points of multiple semi-meridianshaving different surface elevation dimensions may be used to fabricate asingle contact lens.

Referring to FIG. 2 , the center of the pretreatment cornea, and thecenter of the contact lens, are located at the origin of the grid. InFIG. 2 , the front of the pretreatment cornea, and the anterior surfaceof the contact lens (not shown) face downward, toward the bottom of thegrid. The anterior surface, as practiced by those skilled in the art ofcontact lens design and manufacturing, may have a predetermined radiusin a central optic zone for the purpose of creating a predetermined lenspower in conjunction with the posterior surface radius in the centralzone. The anterior optic zone surface may be spherical, aspherical, asingle radius, or multiple radii designed to produce a multifocaloptical power. The peripheral portion of the anterior surface may bedesigned to create a constant thickness from the posterior surface ormay be designed to have varying thicknesses from each correspondingposterior surface control point. The contact lens includes nine controlpoints CP1-CP9, which are related to the zones of the contact lens.However, in other embodiments, different numbers of control points maybe employed.

The central compression zone (CCZ) contacts the pretreatment cornea atits center, and extends from a control point CP1 at the center of thesemi-meridian to a control point CP2, which in this example is locatedat a semi-chord radial distance of approximately 2.5 mm.

Peripheral to the central compression zone is the volume control zone,which extends to control point CP4, which in this example is located ata semi-chord radial distance of approximately 4 mm. The volume controlzone in this example includes two regions. The first region of thevolume control zone (VCZR1) extends to control point CP3, which in thisexample is located at a semi-chord radial distance of approximately 3mm. Peripheral to the first region of the volume control zone is thesecond region of the volume control zone (VCZR2), which includes controlpoints CP6 and CP5, and extends to control point CP4. In this example,control points CP6 and CP5 are located at semi-chord radial distances ofapproximately 3.4 mm and 3.8 mm, respectively.

Peripheral to the second region of the volume control zone is thesecondary compression zone (SCZ), where the contact lens again contactsthe pretreatment cornea. Peripheral to the secondary compression zone isthe peripheral relief zone (PRZ), which includes a control point CP9 andextends to control point CP8, which in this example is located at asemi-chord radial distance of approximately 5 mm. In this example,control point CP9 is located at a semi-chord radial distance ofapproximately 4.5 mm.

Peripheral to the peripheral relief zone is the landing zone (LZ), wherethe contact lens again contacts the pretreatment cornea. The landingzone extends to control point CP7, which in this example is located at asemi-chord radial distance of approximately 5.4 mm. The peripheral endof the landing zone marks the edge terminus (ET) of the contact lens.

A spherical or aspherical base curve may be employed in the centralcompression zone. The volume control zone, the secondary compressionzone, the peripheral relief zone, and the landing zone may be configuredusing circumferentially varied spline mathematics or other geometry toachieve a desired sagittal depth difference at defined control pointsalong each semi-meridian. The elevation difference may be driven bytopographic measurement of the pretreatment cornea at each respectivecontrol point and in each semi-meridian of the cornea to be treated. Theelevation difference between the points on the posterior lens surfaceand the respective points on a pre-treatment corneal surface may utilizean axial distance from the lens surface to the corneal surface or aradial distance from the lens surface to the cornea surface. The axialdistance forms a line parallel to the axis of the lens while the radialdistance is in the direction from the lens surface to a center ofrotation of the corneal surface of the respective eye. In a preferredembodiment, the axial distance from the lens surface to the pretreatmentcorneal surface is used to calculate the elevation difference of thecontrol points on the posterior lens surface and the respective pointson the corneal surface. The lens edge may be reconciled to produce alens that is planar and round, planar and not round, or non-planar andround.

The disclosed contact lens demonstrates improved centration, optimizedreduction in refractive myopia of the treated eye, and a pre-determinedpost-treatment mid-peripheral corneal add power and location. The volumecontrol zone along with the semi-chord radial distance location andangle formed by the secondary compression zone generates the forces toproduce the mid-peripheral add power and location. The peripheral reliefzone allows the secondary compression zone to impinge and redistributethe corneal epithelium inward to the volume control zone. The uniformlyaligned landing zone provides the compression force that produces thecentral compression and the compression within the secondary compressionzone. The rotational asymmetry in the elevation of the landing zone thatmatches the elevation difference of the pretreatment cornea in two ormore semi-meridians provides optimized compression force, lensstability, and improved lens centration. An edge terminus is added tothe landing zone. The shape of the posterior contact lens surface iscontinuous and seamless to avoid any junction induced trauma. In oneembodiment, a cubic spline may be employed with knots placed atcorresponding control points and controls placed to create the smooth,continuous and seamless surface along with the pre-determined areasunder each semi-meridian in the volume control zones and thepredetermined angle inward from the secondary compression zone.

The contact lens is seamless because each zone commences at the localslope of the ending of the zone central to it. The knots of the splineof the volume control zone controls the relative sagittal depth of thelens at defined control points along the posterior surface of thesemi-meridians of the lens outside of the central compression zone whilethe controls of the spline provide for the shape of the surface. Themost central aspect of the spline is defined by the elevation and localslope at the chord of the optic zone junction and the most peripheralaspect is defined by the desired elevation at each next peripheralcontrol point in each semi-meridian. The local slope of the mostperipheral aspect of the volume control zone is defined by thepredetermined squeeze angle with its apex at the deepest point of thesecondary compression zone. The most peripheral aspect of the secondarycompression zone is defined by the local slope of the most centralaspect of the peripheral relief zone; and the most peripheral aspect ofthe peripheral relief zone is defined by the most central aspect of thelanding zone. The edge terminus commences at the elevation of the mostperipheral aspect of the landing zone.

In some applications, the lenses may be custom-designed for each eye. Inother applications, a fitting set may be made from which lenses may beselected. An example fitting set or kit may have one overall diameter(OAD; e.g., in the range of 10.5 mm to 11.5 mm), up to five base curveradii increments (BCRI), each with a single optic zone diameter and onevolume control zone width with up to five volume control zone areas foreach, three secondary compression zone depths for each, one peripheralrelief zone, and one landing zone. This fitting set would have 75 lenses(1 OAD x 5 BCRI x 5 VCZ areas x 3 SCZ depths). A lookup table orcomputer application may be produced to suggest the first fitting setlens by entry of the manifest refraction and the central keratometry orcorneal topography gathered by standard clinical testing.

A preferred empirical method without a fitting set and in the absence ofcorneal topography is to empirically design a first observation lens tobe manufactured by use of the manifest refraction and standardkeratometry to predict the base curve radius; the amount of treatment indiopters and mean biometric data to predict the first and second regionsof the volume control zone; the amount of treatment and mean biometricdata to predict the secondary compression zone depth; standardperipheral relief zone height; and mean biometric data to predict thelocal slope and sagittal depth of the central portion of the landingzone. This first lens designed empirically from clinical data may serveas a lens for observation for ordering a second lens. Note that theempirically designed first observation lens is expected to includerotational asymmetry that is based on biometric mean data that revealthe asymmetry.

FIG. 3 is a flowchart illustrating an overview process 300 for producinga contact lens for corneal reshaping according to some embodiments ofthe disclosed technologies. The elements of the process 300 arepresented in one arrangement. However, it should be understood that oneor more elements of the process may be performed in a different order,in parallel, omitted entirely, and the like. Furthermore, the process300 may include other elements in addition to those presented.

Referring to FIG. 3 , the process 300 may include conducting clinicaltesting of the eye, at 302. The clinical testing may includedetermination of unaided visual acuity, refraction, binocular vision,peripheral refraction, eye health, keratometry, corneal diameter,corneal topography, lid position and aperture size, pupillometry, andthe like.

The process 300 may include selecting constants and calculating lensparameters, at 304. These may include base curve radius, optic zonediameter, overall diameter, mid-peripheral add power, the semi-chordradial distance of the center of the mid-peripheral add power, lenspower, and the like.

The process 300 may include calculating diameters and sagittal depthsfor control points of the posterior surface of the contact lens, at 306.These calculations may be based on biometric mean data, measured cornealtopography, or the like, or combinations thereof. These calculations aredescribed in detail below. Following these calculations, control pointsfor the anterior surface may be calculated, for example using thicknessrules or constants from one or more of the posterior surface controlpoints to one or more of the anterior surface control points andincorporating the required anterior central radius or radii of curvatureto produce the desired lens power or powers in the event of multifocaloptics, or the like.

The process 300 may include creating a cutting file and fabricating acontact lens, at 308. For example, a semi-meridian for the posteriorsurface of the contact lens may be calculated using the control points,for example as shown in FIG. 1 . The semi-meridian surface may begenerated using splines, geometric segments, or the like, orcombinations thereof. The contact lens may be fabricated with usual andcustomary good manufacturing practices from standard extended wear rigidgas permeable material, or the like. For example, a polish-free computernumerically controlled lathe may be employed to cut the contact lens.Cutting may be followed by a contour inspection of the posterior surfaceof the contact lens to determine the finished posterior surface matchesthe intended shape.

The process 300 may include applying and evaluating the contact lenses,at 310. This may include capturing an image of the contact lens on theeye of the patient. The image may be analyzed to assess the lens-eyerelationship and to measure lens centration. The evaluation may includesteps to determine the over-refraction, to measure visual acuity, andthe like. The process 300 may conclude with dispensing the contact lens,and conducting one or more follow-up evaluations, at 312.

FIGS. 4A and 4B are a flowchart illustrating an overview process 400 fordefining a contact lens for corneal reshaping according to someembodiments of the disclosed technologies. The elements of the process400 are presented in one arrangement. However, it should be understoodthat one or more elements of the process may be performed in a differentorder, in parallel, omitted entirely, and the like. Furthermore, theprocess 400 may include other elements in addition to those presented.

Referring to FIG. 4A, the process 400 may include locating a controlpoint CP1 at the geometric center of the lens to correspond with thegeometric center of the pretreatment cornea, at 402. The process 400 mayinclude determining the base curve radius according to manifestrefraction and keratometry of the eye to be treated, selecting adiameter of a control point CP2 as a peripheral terminus of the centralcompression zone CCZ, and setting a sagittal depth of control point CP2at the sagittal depth of the selected base curve radius at the selecteddiameter of control point CP2, at 404.

The process 400 may include selecting a diameter of control point CP3 toseparate a first region of the volume control zone and a second regionof the volume control zone peripheral to the first region of the volumecontrol zone, and set a sagittal depth of control point CP3 at apredetermined diopter distance from the apical radius of thepretreatment cornea, at 406. In one embodiment, the sagittal depthdifference of CP3 from the cornea is intended to be a constant andindependent of the amount of targeted treatment. In this embodiment, alltreatment lenses will have the same sagittal depth difference from theunderlying cornea at CP3 regardless of the differences in the targetedtreatment or the difference between the central corneal radius and theradius of the base curve of the treatment lens. The second region of thevolume control zone is used to accommodate eyes having differentmid-peripheral elevation differences, to equalize the area under eachsemi-meridian, to control the location of the increased corneal powerproduced under this zone, and to improve the centration of the lens. Thecircumferential equalization of area under each semi-meridian eliminatesthe fitting of toric or dual elevation by allowing a non-toric basecurve and a circumferential elevation difference in the volume controlzone to prevent the lens from having heavy bearing on the shallowsemi-meridians of the pretreatment cornea and to prevent z-axis tiltingand decentration toward the deep semi-meridians of the cornea.

The process 400 may include selecting a diameter or semi-chord radialdistance of a control point CP4 for the secondary compression zone toaccording to a desired location of the mid-peripheral add power, at 408.The sagittal depth of the secondary compression zone SCZ at controlpoint CP4 is a function of the sagittal height of the underlyingpretreatment cornea at control point CP4, the apex of the zone. Theposterior surface proceeds to the next control point CP9 to determinethe height of the peripheral relief zone PRZ. In one embodiment theheight of control point CP9 from the underlying pre-treatment cornea isdetermined by the amount of central treatment in diopters. For example,the height of control point CP9 from the underlying cornea may be equalto 6 microns per diopter of treatment. The peripheral relief zone thendescends to a control point CP8. The elevation of control point CP8corresponds to the measured elevation of the pretreatment cornea at thesemi-chord radial distance of the commencement of the landing zone LZ.The semi-chord radial distance of control point CP8 is defined by thesemi-chord radial distance of control point CP7 and a minimum desiredwidth between control points CP8 and CP7. In one embodiment thesemi-chord radial distance of control point CP7 is defined by themeasured horizontal corneal diameter. For example, the lens diameter maybe selected to be 90% of the measured corneal diameter and thesemi-chord radial distance of control point CP7 is then determined to be45% of the corneal diameter. The range of the desired semi-chord widthfrom control points CP8 to CP7 is 0.8 to 1.6 mm. The edge terminus ET atcontrol point CP7 is then integrated into the sagittal depth of the lensat the most peripheral aspect of the landing zone LZ. The sagittal depthof control point CP7 is selected as a function of the known ocularcontour and a pre-selected edge lift from the underlying cornea at thedesired semi-chord radial distance of control point CP7. For example,the desired pre-selected edge lift from the underlying cornea at controlpoint CP7 may be 40 to 80 microns.

The spline for the secondary compression zone SCZ may commence at thelocal slope of the last control point CP5 in the volume control zonespline and may be calculated to create an angle of incidence of thesecondary compression zone SCZ on the underlying pretreatment corneathat optimizes the movement of tissue medially into the volume controlzone, referred to herein as the squeeze angle (SA). The process 400 mayinclude selecting a squeeze angle of a peripheral aspect of the secondregion of the volume control zone, and locating a control point CP5 todefine the squeeze angle with control point CP4, at 410. The angle maybe measured from a line perpendicular to the axis of the lens thatpasses through control point CP4 or may be measured from the local slopeof the underlying cornea at control point CP4. For example, the localslope of the pre-treatment cornea at control point CP4 may be measuredto be 28 degrees and the desired angle between the pre-treatment corneaand the posterior lens surface may be 5 degrees. Thereby, the prescribedangle created by control point CP5 inward from the apex at control pointCP4 and from a horizontal line passing through control point CP4 wouldbe reported as 33 degrees from horizontal.

Referring now to FIG. 4B, the process 400 may include selecting an areaof the volume control zone according to a desired mid-peripheral addpower to determine a location of control point CP6 to create the desiredarea of the volume control zone, at 412. The area of the volume controlzone may be estimated to approximate the area under the posteriorsurface of a second or third generation corneal reshaping lens with a3.00 Diopter target treatment when the lens is placed on a pre-treatmentcornea. Second and third generation CRT lenses are, as a rule, fit about1.00 Diopter longer in radius than the target treatment. Therefore, thetargeted or desired area of a semi-meridian of the volume control zonemay be estimated according to the area under a 4.00 D longer radius ofcurvature lens on a mean cornea with a mean optic zone diameter and meanreverse curve or return zone width; and a mean reverse curve radius orreturn zone depth. The targeted or desired total area under a singlesemi-chord radial distance can include from the center of the lens,control points CP1 to CP4, or the total volume control zone from controlpoints CP2 to CP4, or only the second region of the volume control zone,control points CP3 to CP4. For example, the area from control points CP2to CP4 for a third or fourth generation CRT lens having an optic zonediameter of 5.0 mm; a reverse curve width of 1.5 mm; and a base curveradius of 4.00 Diopters (approximately 0.8 mm longer than the radius ofthe pretreatment cornea) is estimated to be 1.58X10⁴ square microns or0.0158 square millimeters. The desired area in a semi-meridian will varyaccording to the semi-chord radial distance of control points CP2, CP3and CP4. Control point CP4 regulates the semi-chord radial distance ofthe mid-point of the mid-peripheral power addition. The closer to thecenter of the lens the mid-peripheral add power is desired, the shorterthe semi-chord radial distance of control point CP4. The shorter thesemi-chord radial distance of control point CP4, the lower the area ofthe respective volume control zone when control points CP2 and CP3 areheld constant. In one embodiment, the semi-chord radial distance ofcontrol point CP2 is held equal to or greater than 1.5 mm and controlpoint CP3 is held equal to or greater than 2.2 mm. A decreasedsemi-meridian radial distance of control point CP4 decreases thesemi-meridian radial distance of the mid-point of the post treatmentmid-peripheral add power. For a given semi-meridian radial distance ofcontrol point CP4, the greater the area within the volume control zone,the higher the mid-peripheral add power. To be clear, the modulation ofthe semi-meridian radial distance of control point CP4 controls theradial location of the mid-peripheral add power while the area betweenthe posterior lens surface and the pre-treatment cornea within thevolume control zone modulates the mid-peripheral add power. Thesemi-meridian radial distance of control point CP6 modulates the shapeof the mid-peripheral add power.

The process 400 may include determining an overall diameter of thecontact lens according to a corneal diameter of the pretreatment cornea,and determining a location of a control point CP7 according to theoverall diameter of the contact lens, at 414.

The process 400 may include determining a control point CP8 to definethe landing zone LZ to contact the pretreatment cornea according to thecorneal topography of the eye and the location of control point CP7, at416. The circumferential elevation features of the secondary compressionzone SCZ and landing zone LZ results in a uniform edge liftcircumferentially which facilitates improved centration and improvedcomfort. The semi-meridian sagittal depth control design may usedifferent splines in at least one semi-meridian of at least one zone ofthe lens outside of the optic zone. The amount of sagittal depthdifference can be prescribed around a nominal value which is used forthe majority of normal eyes or empirically determined by elevation datafrom corneal topography.

The process 400 may include selecting a diameter of a control point CP9,selecting an area of a peripheral relief zone between the secondarycompression zone and the landing zone, and determining a sagittal depthof control point CP9 according to the selected area of the peripheralrelief zone, at 418. In an alternative embodiment, the sagittal depth ofcontrol point CP9 is determined as a function of the treatment targetfor the respective eye. It is known by those skilled in the art that thecorneal apex retreats approximately 6 microns per diopter of achievedtreatment. Control point CP9 may be placed a distance from theunderlying cornea of 6 microns per diopter. For example, when 3.00 D oftreatment is targeted, control point CP9 may be placed 18 microns fromthe underlying corneal surface when control points CP1, CP4 and CP8 areplaced to contact the corneal surface. Greater clearance is understoodto be acceptable while lesser clearance may impede treatment or requirethe entire lens surface from control points CP4 to CP7 to compress thecornea.

Table 1 below provides an example wherein the semi-meridian cornealelevation at control points at semi-meridian radial distances isprovided and the posterior surface sagittal depths are determinedaccording to the methods of one embodiment of the present invention.

TABLE 1 Description of Control Point Control Point Number ExampleCorneal Elevation mm Lens Semi Chord (x) mm Posterior Lens Sag (z) mmLens to Cornea Clearance (microns) Corneal Apex 1 0.000 0.00 0.000 0Outer boundary or junction of optic zone 2 0.343 2.30 0.313 30 Volumecontrol zone region one outer junction 3 0.403 2.50 0.371 32 Voumecontrol zone area control point 6 0.523 2.80 0.487 36 Volume controlzone inward facing angle control point 5 0.646 3.10 0.628 18 Secondarycompression zone maximum contact point 4 0.732 3.30 0.732 0 Peripheralrelief zone area control point 9 1.005 3.85 0.987 18 Landing zone firstcontact point 8 1.339 4.40 1.339 0 Edge terminus control point 7 2.0735.40 2.013 60 Clinical measurements and design inputs: 1. Treatmenttarget = -3.00 Diopters 2. Flat keratometry = 7.80 mm 3. Base Curveradius = 8.60 mm 3. Corneal diameter = 11.9 mm 4. Radial semi-chorddistance of mid-peripheral add power = 2.8 mm

The process 400 may include defining the semi-chord radial distances andsagittal depths of a semi-meridian of a posterior surface of the contactlens according to control points CP1-CP9, at 420. Following definitionof one or more semi-meridians, the contact lens may be fabricated, forexample as described above. These control point semi-meridian radialdistances and corresponding depths are the inputs for a computer programproduct that completes the required x, y, and z points for the full lenssurface.

The disclosed technologies may be applied to the corneal reshapingportion of corneal rigid lenses as well as the corneal reshaping portionof lenses having a diameter greater than the cornea, for exampleincluding scleral contact lenses, hybrid contact lenses and soft contactlenses. The edge terminus is not connected to the anterior surface atcontrol point CP7 for embodiments where the lens has a diameter greaterthan the cornea. Rather, the terminus of the peripheral landing zone isconnected to a next peripheral zone on the posterior surface thatextends beyond the diameter of the cornea in at least one semi-meridian.

FIG. 5 depicts a block diagram of an example computer system 500 inwhich embodiments described herein may be implemented. The computersystem 500 includes a bus 502 or other communication mechanism forcommunicating information, one or more hardware processors 504 coupledwith bus 502 for processing information. Hardware processor(s) 504 maybe, for example, one or more general purpose microprocessors.

The computer system 500 also includes a main memory 506, such as arandom access memory (RAM), cache and/or other dynamic storage devices,coupled to bus 502 for storing information and instructions to beexecuted by processor 504. Main memory 506 also may be used for storingtemporary variables or other intermediate information during executionof instructions to be executed by processor 504. Such instructions, whenstored in storage media accessible to processor 504, render computersystem 500 into a special-purpose machine that is customized to performthe operations specified in the instructions.

The computer system 500 further includes a read only memory (ROM) 508 orother static storage device coupled to bus 502 for storing staticinformation and instructions for processor 504. A storage device 510,such as a magnetic disk, optical disk, or USB thumb drive (Flash drive),etc., is provided and coupled to bus 502 for storing information andinstructions.

The computer system 500 may be coupled via bus 502 to a display 512,such as a liquid crystal display (LCD) (or touch screen), for displayinginformation to a computer user. An input device 514, includingalphanumeric and other keys, is coupled to bus 502 for communicatinginformation and command selections to processor 504. Another type ofuser input device is cursor control 516, such as a mouse, a trackball,or cursor direction keys for communicating direction information andcommand selections to processor 504 and for controlling cursor movementon display 512. In some embodiments, the same direction information andcommand selections as cursor control may be implemented via receivingtouches on a touch screen without a cursor.

The computing system 500 may include a user interface module toimplement a GUI that may be stored in a mass storage device asexecutable software codes that are executed by the computing device(s).This and other modules may include, by way of example, components, suchas software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables.

In general, the word “component,” “engine,” “system,” “database,” datastore,” and the like, as used herein, can refer to logic embodied inhardware or firmware, or to a collection of software instructions,possibly having entry and exit points, written in a programminglanguage, such as, for example, Java, C or C++. A software component maybe compiled and linked into an executable program, installed in adynamic link library, or may be written in an interpreted programminglanguage such as, for example, BASIC, Perl, or Python. It will beappreciated that software components may be callable from othercomponents or from themselves, and/or may be invoked in response todetected events or interrupts. Software components configured forexecution on computing devices may be provided on a computer readablemedium, such as a compact disc, digital video disc, flash drive,magnetic disc, or any other tangible medium, or as a digital download(and may be originally stored in a compressed or installable format thatrequires installation, decompression or decryption prior to execution).Such software code may be stored, partially or fully, on a memory deviceof the executing computing device, for execution by the computingdevice. Software instructions may be embedded in firmware, such as anEPROM. It will be further appreciated that hardware components may becomprised of connected logic units, such as gates and flip-flops, and/ormay be comprised of programmable units, such as programmable gate arraysor processors.

The computer system 500 may implement the techniques described hereinusing customized hard-wired logic, one or more ASICs or FPGAs, firmwareand/or program logic which in combination with the computer systemcauses or programs computer system 500 to be a special-purpose machine.According to one embodiment, the techniques herein are performed bycomputer system 500 in response to processor(s) 504 executing one ormore sequences of one or more instructions contained in main memory 506.Such instructions may be read into main memory 506 from another storagemedium, such as storage device 510. Execution of the sequences ofinstructions contained in main memory 506 causes processor(s) 504 toperform the process steps described herein. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions.

The term “non-transitory media,” and similar terms, as used hereinrefers to any media that store data and/or instructions that cause amachine to operate in a specific fashion. Such non-transitory media maycomprise non-volatile media and/or volatile media. Non-volatile mediaincludes, for example, optical or magnetic disks, such as storage device510. Volatile media includes dynamic memory, such as main memory 506.Common forms of non-transitory media include, for example, a floppydisk, a flexible disk, hard disk, solid state drive, magnetic tape, orany other magnetic data storage medium, a CD-ROM, any other optical datastorage medium, any physical medium with patterns of holes, a RAM, aPROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip orcartridge, and networked versions of the same.

Non-transitory media is distinct from but may be used in conjunctionwith transmission media. Transmission media participates in transferringinformation between non-transitory media. For example, transmissionmedia includes coaxial cables, copper wire and fiber optics, includingthe wires that comprise bus 502. Transmission media can also take theform of acoustic or light waves, such as those generated duringradio-wave and infra-red data communications.

The computer system 500 also includes a communication interface 518coupled to bus 502. Network interface 518 provides a two-way datacommunication coupling to one or more network links that are connectedto one or more local networks. For example, communication interface 518may be an integrated services digital network (ISDN) card, cable modem,satellite modem, or a modem to provide a data communication connectionto a corresponding type of telephone line. As another example, networkinterface 518 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN (or a WAN component tocommunicate with a WAN). Wireless links may also be implemented. In anysuch implementation, network interface 518 sends and receiveselectrical, electromagnetic or optical signals that carry digital datastreams representing various types of information.

A network link typically provides data communication through one or morenetworks to other data devices. For example, a network link may providea connection through local network to a host computer or to dataequipment operated by an Internet Service Provider (ISP). The ISP inturn provides data communication services through the world wide packetdata communication network now commonly referred to as the “Internet.”Local network and Internet both use electrical, electromagnetic oroptical signals that carry digital data streams. The signals through thevarious networks and the signals on network link and throughcommunication interface 518, which carry the digital data to and fromcomputer system 500, are example forms of transmission media.

The computer system 500 can send messages and receive data, includingprogram code, through the network(s), network link and communicationinterface 518. In the Internet example, a server might transmit arequested code for an application program through the Internet, the ISP,the local network and the communication interface 518.

The received code may be executed by processor 504 as it is received,and/or stored in storage device 510, or other non-volatile storage forlater execution.

Each of the processes, methods, and algorithms described in thepreceding sections may be embodied in, and fully or partially automatedby, code components executed by one or more computer systems or computerprocessors comprising computer hardware. The one or more computersystems or computer processors may also operate to support performanceof the relevant operations in a “cloud computing” environment or as a“software as a service” (SaaS). The processes and algorithms may beimplemented partially or wholly in application-specific circuitry. Thevarious features and processes described above may be used independentlyof one another, or may be combined in various ways. Differentcombinations and sub-combinations are intended to fall within the scopeof this disclosure, and certain method or process blocks may be omittedin some implementations. The methods and processes described herein arealso not limited to any particular sequence, and the blocks or statesrelating thereto can be performed in other sequences that areappropriate, or may be performed in parallel, or in some other manner.Blocks or states may be added to or removed from the disclosed exampleembodiments. The performance of certain of the operations or processesmay be distributed among computer systems or computers processors, notonly residing within a single machine, but deployed across a number ofmachines.

As used herein, a circuit might be implemented utilizing any form ofhardware, or a combination of hardware and software. For example, one ormore processors, controllers, ASICs, PLAs, PALs, CPLDs, FPGAs, logicalcomponents, software routines or other mechanisms might be implementedto make up a circuit. In implementation, the various circuits describedherein might be implemented as discrete circuits or the functions andfeatures described can be shared in part or in total among one or morecircuits. Even though various features or elements of functionality maybe individually described or claimed as separate circuits, thesefeatures and functionality can be shared among one or more commoncircuits, and such description shall not require or imply that separatecircuits are required to implement such features or functionality. Wherea circuit is implemented in whole or in part using software, suchsoftware can be implemented to operate with a computing or processingsystem capable of carrying out the functionality described with respectthereto, such as computer system 500.

As used herein, the term “or” may be construed in either an inclusive orexclusive sense. Moreover, the description of resources, operations, orstructures in the singular shall not be read to exclude the plural.Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. Adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known,” and terms of similar meaning should not beconstrued as limiting the item described to a given time period or to anitem available as of a given time, but instead should be read toencompass conventional, traditional, normal, or standard technologiesthat may be available or known now or at any time in the future. Thepresence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent.

1. A contact lens for reshaping a pretreatment cornea of an eye of apatient, comprising: an anterior surface; and a posterior surface havinga semi-meridian defining: a central compression zone to contact thepretreatment cornea, a volume control zone peripheral to the centralcompression zone, wherein: the volume control zone is defined by atleast four geometric control points connected by one of a spline, apolynomial, or a combination of conic sections and uncurved segments, asecond geometric control point is peripheral to a first geometriccontrol point, a third geometric control point is peripheral to thesecond geometric control point, and a fourth geometric control point tocontact the pretreatment cornea, wherein the fourth geometric controlpoint is peripheral to the third geometric control point, a secondarycompression zone to contact the pretreatment cornea, wherein thesecondary compression zone is peripheral to the volume control zone, aperipheral relief zone peripheral to the secondary compression zone, alanding zone to contact the pretreatment cornea, wherein the landingzone is peripheral to the peripheral relief zone, and an edge terminusperipheral to the landing zone.
 2. The contact lens of claim 1, whereina radius of the central compression zone is spherical.
 3. The contactlens of claim 1, wherein a radius of the central compression zone isaspherical.
 4. The contact lens of claim 1, wherein a diameter of thecentral compression zone is between 3.0 and 7.0 mm.
 5. (canceled)
 6. Thecontact lens of claim 1, wherein: the first geometric control point ofthe volume control zone is positioned to have a z-axis separation fromthe pretreatment cornea in a range of 5 and 80 microns.
 7. The contactlens of claim 1, wherein: the second geometric control point of thevolume control zone is positioned to have a z-axis separation from thepretreatment cornea that defines a predetermined area between theposterior surface and the pretreatment cornea in the volume controlzone.
 8. The contact lens of claim 1, wherein: the third geometriccontrol point of the volume control zone is positioned to define apredetermined angle between (i) a line connecting the third and fourthcontrol points and (ii) a horizontal line through the fourth controlpoint.
 9. The contact lens of claim 1, wherein: a semi-chord radialdistance of the fourth geometric control point is in a range of 2.6 mmto 5.2 mm.
 10. The contact lens of claim 1, wherein: the secondarycompression zone has a width in a range of 0.2 mm to 0.8 mm.
 11. Thecontact lens of claim 1, wherein: the secondary compression zone isdefined by a shape having at least one control point within thesecondary compression zone, the shape defined by one of: a spline; apolynomial; or a convex conic section.
 12. The contact lens of claim 1,wherein: the peripheral relief zone is defined by at least one controlpoint positioned to have a z-axis separation from the pretreatmentcornea that is at least 6 microns per diopter of attempted reduction ofcentral refractive error.
 13. The contact lens of claim 1, wherein: theperipheral relief zone has a width of between 0.4 mm and 1.2 mm.
 14. Thecontact lens of claim 1, wherein: the peripheral landing zone is definedby a shape having at least one control point within the peripherallanding zone, the shape defined by one of: a spline; a polynomial; aconic section; an angled curved section; or an angled uncurved section.15. The contact lens of claim 1, wherein: an edge terminus of theposterior surface commences at the most radially peripheral aspect ofthe peripheral landing zone and connects to the most peripheral aspectof the anterior surface; and the edge terminus of the posterior surfaceis defined by: an ellipse, a conic section, or a spline.
 16. The contactlens of claim 1, wherein: the volume control zone and the secondarycompression zone are defined by a single spline.
 17. A method fordefining a contact lens to be manufactured for an eye of a patient, themethod comprising: selecting, according to corneal topography of the eyeof the patient: a base curve radius of a central compression zone of thecontact lens, a peripheral semi-meridian radial distance of the centralcompression zone of the contact lens, an area of a volume control zoneadjacent to the central compression zone, and a semi-chord radialdistance of a secondary compression zone to contact a pretreatmentcornea of the eye, wherein the secondary compression zone is adjacentand peripheral to the volume control zone; determining locations of aplurality of control points to define at least the central compressionzone width, the area of the volume control zone, and the semi-meridianradial distance of the secondary compression zone; and defining asemi-meridian of a posterior surface of the contact lens according tothe plurality of control points.
 18. The method of claim 17, furthercomprising: locating a first one of the control points at the geometriccenter of the contact lens and the corresponding geometric center of thepretreatment cornea.
 19. The method of claim 18, further comprising:determining the base curve radius according to manifest refraction andkeratometry of the eye; selecting a semi-chord radial distance of asecond one of the control points as a peripheral terminus of the centralcompression zone; and setting a sagittal depth of the second one of thecontrol points at the sagittal depth of the selected base curve radiusat the selected semi-chord radial distance of the second one of thecontrol points while the first one of the control points is in contactwith the underlying pretreatment cornea.
 20. The method of claim 19,further comprising: selecting a semi-chord radial distance of a thirdone of the control points to separate a first region of the volumecontrol zone and a second region of the volume control zone peripheralto the first region of the volume control zone; and setting a sagittaldepth of the third one of the control points at a distance equal to thedistance of a lens having a predetermined diopter treatment targetradius when placed on a mean pretreatment cornea.
 21. The method ofclaim 20, further comprising: selecting a semi-chord radial distance ofa fourth one of the control points equal to the semi-chord radialdistance of an apex of the secondary compression zone according to adesired mid-peripheral add location.
 22. The method of claim 21, furthercomprising: selecting a squeeze angle of a peripheral aspect of thesecond region of the volume control zone; and locating a fifth one ofthe control points to define the squeeze angle with the fourth one ofthe control points.
 23. The method of claim 22, further comprising:determining a location of a sixth one of the control points according tothe selected area of the volume control zone according to the desiredmid peripheral add power.
 24. The method of claim 23, furthercomprising: determining an overall diameter of the contact lensaccording to a corneal diameter of the pretreatment cornea; anddetermining a location of a seventh one of the control points accordingto the overall diameter of the contact lens.
 25. The method of claim 24,further comprising: determining an eighth one of the control points todefine a medial aspect of a landing zone to contact the pretreatmentcornea according to the corneal topography of the eye and the desiredradial distance from the seventh one of the control points according tothe desired radial width of a landing zone.
 26. The method of claim 25,further comprising: selecting a diameter of a ninth one of the controlpoints; selecting an area of a peripheral relief zone between thesecondary compression zone and the landing zone; and determining asagittal depth of the ninth one of the control points according to theselected area of the peripheral relief zone or according to the targetedtreatment in diopters.
 27. The contact lens of claim 8, wherein thepredetermined angle has its apex at the fourth control point.
 28. Thecontact lens of claim 27, wherein the apex has a z axis location that isintended to contact the cornea simultaneously with the center of thecentral compression zone.